[Bug rtl-optimization/41849] New: optimization fails when register variables are used for an interrupt

["hendrixgr at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

If i use global register variables that are used and updated inside an
interrupt the optimizer produces broken code.
Code example:
register volatile unsigned char  timer0_h8 asm("r3");
volatile unsigned char timer0_h8_buf = 0;

void foo(void)
{
timer0_h8_buf = timer0_h8; 

return;
}

ISR(TIMER0_OVF_vect)
{
   timer0_h8++;
}  

produces:

2432 0b5a 1092 0000  sts timer0_h8_buf,__zero_reg__      ;  timer0_h8_buf,

instead of this when no optimization is used:

3248 104a 832D                  mov r24,r3       ;  timer0_h8.47, timer0_h8
3249 104c 8093 0000             sts timer0_h8_buf,r24    ;  timer0_h8_buf,
timer0_h8.47


-- 
           Summary: optimization fails when register variables are used for
                    an interrupt
           Product: gcc
           Version: 4.4.2
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hendrixgr at gmail dot com
 GCC build triplet: Linux i386
  GCC host triplet: Linux ubuntu 9.04
GCC target triplet: avr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41849